Virtual Private Network (VPN) is a technology of constructing a private network on a public network through tunneling, encryption, decryption, and authentication. The VPN technology is characterized by low costs, high security, high extensibility, manageability, and comprehensive control, and is a trend of enterprise networks. Unlike a traditional network, a VPN does not exist physically, but uses the existing public network to construct a virtual network through resource configuration. A VPN is a logical network exclusively accessible to a specific enterprise or user group. The VPN is not a simple upper-layer service, but is an interconnected network between private network users. Tunneling protocols of the VPN include Layer 2 Tunneling Protocol (L2TP), Security Architecture for IP network (IPSec) protocol, and Generic Routing Encapsulation (GRE) protocol. The tunneling protocol of the VPN uses a tunneling technology on the protocol layer. A tunnel is a virtual point-to-point connection. In practice, a tunnel may be regarded as a virtual interface that supports only point-to-point connections. This interface provides a path through which the encapsulated data packets can be transmitted. The data packets are encapsulated and decapsulated on both ends of a tunnel.
In the process of applying the VPN tunneling protocol to process packets, a distributed architecture of multiple service boards is generally in use. In such architecture, a main control board is responsible for negotiating and setting up tunnels, and processing packets. The workload of the main control board increases with the increase of negotiation and setup of tunnels and the increase of packets. That reduces the service throughput of the whole architecture and the efficiency of processing the packets.